Phase comparison apparatus



May 7, 1946. R. M. BowlE PHASE COMPARISON APPARATUS Filed May 26, 1943 5 Sheets-Sheet 1 I I I I I I i I I I i l i I z I I I/ l INVENTOR May 7, 1946. R. M. BowlE 2,399,66l

PHASE COMPARISON APPARATUS Filed May 26, 1945 5 Sheets-Sheet 2 5 Sheets-Sheet 3 W Q i www INVENTOR oef/P-r /7 ,50W/- ATT R. M. BOWIE PHASE COMPARISON APPARATUS Filed May 26, 1943 QN @QQ May 7, 1946.

May 7, 1946 R. M. BoWlE 2,399,661

PHASE COMPARI SON APPARATUS Filed May 26, 1945 5 Sheets-Sheet 4 BY ag ATToRNE May 7, 1946. R. M. BowlE- 2,399,661

PHASE COMPARI SON APPARATUS Filed May 26, 1945 5 Sheets-Sheet 5 746 INVENTOR /f/Pr /7 50W/f:

BY M

.x ATTORNE Patented May 7, 1946 Unirse stares earaur ortica Robert M. Bowie, Emporium, Pa., assigner to Sylvania Electric Products Inc., Emporium, Pa., a corporation of Massachusetts Application May ze, 1943, serial Nn. issues 4s claims. (ci. 35-1) This invention refers to electrical signaling circuits including electron discharge tubes, and in particular, to tubes and circuits for detecting and adjusting the coincidence of a plurality of pairs of electrical quantities such as voltages, currents, and phase differences. One aspect of this invention refers to cathode ray tubes; another to the generation and detection of electrical signals and their interpretation as angles and distances.

'Signals of this type are received and decoded by a certain class of radio locators known as radars, in which angles (as azimuth and elevation of an object) are directly read by adjusting 1 the angles of directive antennae to maximum reception, and distances are obtained by adjusting lthe phase angle between periodically transmitted if obtained with undue delay. Radar operators must therefore be highly trained before attaining the necessary degree of speed and accuracy for this purpose. This training can be carried out with the help of training unit, in which signals of arbitrarily chosen values, similar to those received by the actual radio locator, are produced at will and are injected into a students operating unit on which the student performs the same manipulations as on the actual locating device and seesV the same kind of display. Itv is, of course, desirable that a large number of pupils be trained simultaneously from a single signal source and that the nature of the signals be as realistic as possible.

The devices so far available for this purpose do not fulfill these requirements, in that the number of student stations operable from the same master or generating unit, and the number of effects attainable by the signal generator are very limited, particularly as to the simulation of reflections from several objects at dierent apparent azimuth and range positions. This is substantially due to the fact that these prior training units are almost entirely mechanical in their action. The invention avoids these disadvantages by the use of a completely electrical signaling equipment, which incorporates only those mechanical parts which correspond to the ones provided in the actual radio locators, such as the dials and knobs for rotating directive antennae and for adjusting phase differences.

One important circuit element in my new training unit is a cathode ray tube which is so deslgnedthat one of its circuits becomes conducfor double coincidence detection in Awhich means' tive only after signals which tend to produce an arbitrarily given deflection of the cathode ray beam in two mutually perpendicular directions are compensated-by similar separately controllable signals. The first named signals may be two voltages applied to one plate in each of two pairs of deiiection plates. The second named signals may be two voltages applied plates in each pair. g

It is therefore an object yof the invention to provide a tube capable of detecting a double coincidence.

It is another object of the invention to provide means for transmitting and detecting infomation referring to an angle.

According to a further object of the invention, means are provided for simulating to a student the type of infomation normally provided by a radar regarding distances to, and azimuth. of, each of several objects and the effects of Various spurious signals.

Another feature refers to the ease with which the new equipment can be adaptedto the simulation of multiple echoes and ofarbitrary noise eiects similar to those occurring in actual radio locating devices.

It is still further an object of the invention to provide means whereby the student can manipulate angular adjustments and obtain the eect of the reception of a directional antenna array.

A feature of the invention refers to means for simulating to a student the eiects obtained by equalizlng two echo responses received by a pair of antennae which bear a slight angular displacement with respect to each other. l

A further feature refers to a cathode ray tube are provided for correcting errors which may result from the earth magnetic field or from other A plates.

According to another feature, the external field may be compensated by locating a masked photocell in the proper position on the uorescent screen of an ordinary cathode ray tube which may be used as a detector.

While one aspect of my invention covers the detection and 'generation of information concerning an angle in a radar trainer by means of D. C. voltages applied to the deflection plates of to the other cathode ray tubes, it is also intended to cover alternate means for accomplishing those purposes iin conjunction with the training elements for determining the distances of remote objects) These alternate means provide for the matching of phases of two waves fed over two or more different paths from a common source of high irequeucy oscillations, by use of circuits containing various known types of radio tubes and phasing means to be described.

Several embodiments of this part of the invention will be discussed in connection with Figs. 10, 11 and 12. One of these embodiments refers to the type of signal received with a single rotating antenna as explained in the discussion of Figs. 2 and 4. The other one is especially adapted to the reception oi signals of the type referred to in Figs. 3 and 5.

The principal objects of this portion of the invention may therefore be summarized by the following features.

(1a) The development of two sinusoidal voltages, the phases of which-are under the control of master and student respectively.

(2a) The addition and subsequent rectification of said sinusoidal voltage in such a way that a rectified sign-a1 is obtained which is a minimum, preferably zero, when a predetermined phase relationship exists between the two sinusoidal waves. This predetermined phase relationship may be 180.

(3a) The control of the gain of a stage of amplification through which another signal is passed such that the strength of that output signal may be maximized by shifting the phase of one sinusoidal signal with respect to the other.

Furthermore:

(1b) The simultaneous development of two D. C. voltages in the manner just described under (1a) and (2a) above, either of which may be maximized separately by the control of the phase of one sinusoidal voltage with reference to the phase of one of two other sinusoidal voltages whose phases differ by a predetermined amount.

(2b) The control of the gain of two stages of amplification through which another signal passes in parallel, these stages also being provided with means which alternately paralyze one or another of them, since their outputs are in parallel.

My invention will be best understood by a detailed description in connection with the drawings in which:

Fig. 1 is a perspective View of one type of double coincidence detecting tube with part of the envelope broken away to show the electrode arrangement and a schematic diagram of the circuits associated with the tube elements.

Figs. 2 and 3 show response curves obtained from two kinds of directional antennae,

Figs. 4 and 5 show the forms of the corresponding kinds of signals appearing on an oscilloscope screen as a result of the response diagrams of Figs. 2 and 3.

Fig. 6 is a circuit diagram, partly schematic, of a trainer unit which is capable of simulating the signals received by two directional antennae whose response curve is given in Fig. 3.

Fig. 'l is a more detailed circuit diagram of part of Fig. 6.

Fig. 8 shows a double coincidence detector tube in which compensating deflection electrodes are provided for correcting errors due to external Fig. 9 shows another arrangement of tubes which can be used for manipulating an ordinary cathode ray tube with :fluorescent screen as a double coincidence detector in cooperation with a movable masked photocell whose position on the screen may be adjusted for correcting the effect of external fields.`

Figs. l0, 11 and l2 refer to another embodiment of the invention in which the simulation of the azimuth operation is carried out by circuits using conventional radio tubes in place of the special cathode ray tube described in connection with Figs. 1 and 7. In Fig. 10, a basic azimuth circuit is shown which may be used in place of that used in Fig. 1. In Fig. 11, details are shown of the master phasing circuit used in the circuit of Fig. 12. Fig. 12 shows a circuit diagram of anazimuth trainer with double peaks corresponding to the circuit explained in connection with the Figs. 3, 5 and 6. In place of the special cathode .ray tube shown in these earlier figures, various types of standard radio tubes are shown in Fig. 11.

Referring to Fig. 1, the tube I is in the form of an elongated glass bulb or envelope having an electron gun mounted at one end for developing a beam of electrons. This gunv may be of any construction well-known in the cathode-ray tube art and comprises, for example, an electron-emitting cathode 2, control electrode 3, rst accelerating and focussing anode 4, and a second accelerating and focussing anode 5. Supported on the sealed-in wires 6 and 1 are the two'spaced electrostatic beam deflector plates 8 and 9; and supported on the sealed-in wires I0, II, are the additional set of beam deector plates I2, I3. Plates 8 and 9 are mounted in planes at right angles to the planes of plates I2 and I3, in the well known manner. Mounted at the opposite end of tube I is a centrally perforated metal plate or baille I4, and a hollow cylindrical metal cup or collector electrode I5. Electrodes 2 to 5, I4 and I5, are mounted so that they are in axial alignment, with the aperture I6 in line with the gun aperture I1, and with the plates 8, 9, and I2, I3, symmetrically positioned with respect to the axial line between the said apertures.

When the tube is in operation, the focussed l electron beam B emerging from gun aperture I1 passes between the deflector plates and strikes either the plate I4 or collector I5. When the potential on deflection plate 8 with reference to the second anode of the gun is equal to that of plate 9, the beam passing between them will remain undeflected. In like manner when the potential of the electrode I2 is equal to that of electrode I3, the beam continues undeiiected in a straight line and passes through the aperture I6, thus causing an output signal from collector I5. Therefore, the described tube is capable of use as a double coincidence detector. yIf the potential of deection plate 8 is not equal to that of plate 9 or if that of I2 is not equal to that of I3, no output signal is released from col-v lector I5. It should be further notedfthat when the beam B is passing through the aperture I6, it is possible to transmit intelligence along the beam B to the collector I5 under control of grid A 3. The beam may, for instance, be modulated by code or by impulses of any desired shape.

The tube as just described, when associated with certain circuits, may be used to indicate the coincidence of an angle setting on the control dial of one circuit, with an angle setting on the f control dial of another circuit. For this pur4 pose, any arrangement may be used which automark 39 of the oscilloscope. By rotating the azimuth knob 21 he may then bring the shorter matically produces pairs of voltages in response to an angular dial setting, which are proportional to the sin and cos of that angle. In the embodiment of Fig. 1, this is accomplished by impressing the voltage from battery I1M across the potentiometers IBM and ISM. A crank arrangement 20M actuated from the master azimuth knob 2IM, causes contacts on the two potentiometers to be .positioned according to the sin and cos of the angle set von the azimuth knob. In this way, the two desired voltages with reference to the second anode of the gun are supplied to deection plates 9 and I3. At the students position, indicated by the dotted line I, a similar arrangement of battery 23, potentiometers 24 and 25, and crank 26 is provided. For obtaining the desired double coincidence, the student rotates his azimuth knob 21 until the potentials on plates 8 and l2 are equal to those supplied by the master to plates 1 and I3. At this setting of the angle of the students azimuth knob beam, B will pass through the aperture I6. The current collected-by. catcher I may be indicated on an oscilloscope 28 as shown in Fig. l, or by a microammeter or other indicating device.

Inasmuch as the diameter of beam B and the diameter of the aperture I6 are of iinite size, there is a range of angles over which current may be collected at collector I5. If this current is plotted as a function of the students azimuth setting, a diagram as shown in Fig. 2 is obtained when the azimuth of the master dial is xed at the value indicated by 29 in Fig. 2.

In view of the similarity between the.curve just described in connection with Fig. 2, and that obtained from a directional antenna of a radar, the usefulness of this tube and circuit arrangement in training radar operators becomes clear. The azimuth of a fictitious object can be set on the master azimuth dial 2IM and may be detected by the student by rotating his azimuth knob 21.

In the operation of radars, usually brief periodic pulses of radio Waves are transmitted, whose echoes from the eld of view are received together with the originally transmitted signal. The range of each object is determined by the echo time. To simulate the eiect of range, it is therefore only necessary to produce a pulse wave 30 from a suitable master oscillator 3| and apply it to a phase delay circuit 32, the delay of which is under control of the master. The output 'of phase circuit 32 is then fed to a Suitable attenuator 33 and from there to the grid 3 of the electron gun as shown. Thus, the pulses 3,4 applied to grid 3 are of smaller amplitude and phase delayed with relation to pulses 30. Pulses 30 are also fed to another phase delay circuit 36 which isunder the control of the student. The output of phase delay circuit 36 is used for initiating the horizontalvscan on oscilloscope 28 by any well-known means. The vertical scan of the oscilloscope is derived by adding the signal reaching collector I5 to the original signal 30 thus producing a composite signal 35.` The tall pulses are those produced by signal 30 and represent the directly received transmitter pulses. The interspersed smaller pulses 34 are derived from collector I5 and are variable in amplitude and position relative to the tall ones. They represent echoes. The student can now adjust the zero setting of his range scale on the oscilloscope screen by adjusting the range knob 38 so as to locate the unattenuated pulses 30 on the index echo pulse 34 to a maximum on his oscilloscope screen. and thus determine the azimuth angle. Finally, by rotating the range knob 38 until the echo pulse coincides with the index mark, he can determine the range.

Although the-description given in connection' i with Fig. 1 refers to a single student unit connected to the master unit and the circuit shown in Fig. 1 provides only a single echo, it is obvious that a large number of student units could be operated from a single master unit. The master unit comprises all parts marked with an M, phase delay circuit 32 and the attenuator 33. All other components, including the double coincidence detectingtube, must be duplicated at each student unit. In order to simulate multiple echoes, itis, of course, necessary to duplicate the master echo equipment for each additional echo.

In operating the trainer unit described above, the student determines the azimuth by adjusting the response of the echo 34 upon the oscilloscope screen to a maximum'. This adjustment is obtained by rotating the azimuth knob 21 back and forth about the maximum position. This operation corresponds to the determination of azimuth used in one type of radar. In other types of radars a more accurate method is used for the determination of the azimuth. Instead of a single antenna with a response such as shown in Fig. 2,-the more accurate method provides two antennae displaced from each other by a small angleand rotatable as a unit. The response diagram of this arrangement is 'shownin Figs. 3 and 5. The intensity response of one antenna is given -by curve A, that of the other one by curve B of Fig. 3. In this type of reception, it is customary to receive alternately upon one antenna and then upon the other. Assume that an object in the direction indicated by line 29 in Fig. 3 has been located. Following the wave pulse transmitted at a certain instant an echo is received on antenna A corresponding to a point on lobe curve B. The relative sizes of the two responses are then compared by the operator by the means described in connection with Figs. 5 and '1. By rotating the assemblyas a unit, it is possible to equalize the responses received by the two antennae A and B. For equal response on the two antennae, the object lies along the line bisecting the angle dened by the maxima of the lobe curves A and B in Fig. 3. For determining the equality of the two responses, reference is now made to Fig. 5 which represents a view of the oscilloscope screen. Consider the instant of time when a signal is received on antenna A, vand assume that the corresponding scan on the cathode ray tube screen started at the point marked A start and progressed towards the right, producing the peak mark A in Fig. 5 when the echo is received. When the antenna switch is shifted to receive from antenna B, a small Afixed D. C. voltage is applied to the horizontal deflection plates in the oscilloscope so that the corresponding scan starts a B start and progresses to the right giving the slightly displaced peak mark B when the echo is received on antenna B. This process of switching antennae repeats itself indenltely. Accordingly, the two peak marks, A

and B, appear stationary and close to each otherbly. When the heights of A and B appear equal on the oscilloscope screen, the antenna assembly is directed towards the object.

To achieve this effect in a radar trainer accordin'g to the invention, it is necessary to devise means for quickly changing the two voltages which are applied to the electrodes 8 and I2 of the tube shown in Fig. 1. One way of doing this would be to use, at the student unit, two sets of sinusoidal potentiometers ganged together but displaced by a slight angle with respect to each other and to provide rapidly operating mechanical switches. This, however, is impractical'because the rate of switching is too high for mechanical contacts. It is possible, however, to avoid mechanical switching altogether, and to obtain the desired effect by a method based Yon certain properties of the sin and cos of the sum and difference of two angles. Take the wellknown relation:

cos (iA) (cos 0. cos A) :(sin 0. sin A0) vIf A0 is a small angle, the above formula yields theapproximation:

cos (eiA) :cos 01A@ sin 0 In like manner, it can be shown that sinwino) :sin @i0 cos 0 Therefore, in order to achieve the desired shifting of angle, it is only necessary to add to and then to subtract from the voltage representing cos 0 a small voltage which is proportional to sin 0, as A0 is a small constant. The sine voltage applied to the other plate is manipulated correspondingly. One arrangement for achieving these results is shown in Fig. 6, wherein parts corresponding in function to those in Fig. 1, bear the same designation numerals. In addition to the parts of Fig. 1, there are shown in schematic form, 4apparatus and circuit connections for adding to the voltage applied to the plates 8, 9, I2 and I3 of tube I, two other small voltages, namely i-Ao cos 0M and in@ sin 0M. For this latter purpose, the crank 26 also controls a movable tap 40 which supplies a voltage sin 0 to the electronic switch 44. At thesarne time, there is delivered over contact arm 22M a voltage sin s to the electronic switch 46. The switches 44 and 46 are controlled by respective square-Wave signals 54, 55, derived from the same master oscillator source 3| but are 180 degrees out of phase. For this latter purpose, a portion of the output of the phase adjuster 36 is changed in frequency by a frequency divider D to one-half the input frequency as described for example in application Serial No. 453,367, filed August 3, 1942. These divided frequency waves are then passed through a wave Shaper SH to convert them into square waves as indicated. A portion of the output of device SH is applied to switch 44. Another portion is applied to an inverter 1N Whereby the output Waves of the inverter are displaced 180 degrees with respect to the input waves. As a result, the switches 44 and 46 are alternately conductive and produce a series of waves corresponding respectively to A@ sin 0 and A0 sin 6. These latter signals are then impressed upon the plate 9 of the tube I together with the cos 0M waves directly from the potentiometer ISM so that the resultant voltage applied to plate 9 is cos (0M-LM). Likewise, the potentiometer ISM feeds another pair of electronic switches 44a, 46a, similar toswitches 44 and 46, switches 44a and 46a being also fed with signals 54 and 55, with the result that there is applied t0 the plate I3 of the tube I signals represented by :A0 c'os an as well as the'direct signal sin au. The resultant signal on plate I3 is therefore sin (suino). The resultant signals applied to plates 8 and I3 as above described reproduce the conditions correspending to a shifting of an angle of a pair of directional antennae4 of a radar,device as described above in connection with Figs. 3 and 5.

Fig. 7 shows in somewhat more detail the circuit connections for controlling the pair of electronic switches 44 and 48 under control of the sin potentiometer IBM with its crank 26. The crank 26 in addition to varying the main sin and cos arms 22M and 28M also varies another pair of arms 40 and 4I. The arm 48 is connected to a high resistance potentiometer 42 and from thence through potentiometer arm 43 to the control grid of a pentode 44 which acts as one of the electronic switches. This applies a voltage sin 0 to the control grid of tube 44. Another voltage tapped ofi by contact 22M and proportional to -sin 6 is divided by a high resistance potentiometer 45 and is fed to the control grid of pentode 46. Either one or the other of these tubes is caused to become conducting by the application of the square waves 54, 55, (Fig. 6) to their respective suppressor grids. Fixed maximum potentials of the suppressor grids (with respect to the cathode) are determined by means of resistors 41 and 48, condensers 49, and double diode 50. When tube 46 is conducting, a small voltage proportional to sin 0 is added through condenser 51 to the undivided voltage proportional to cos 0 from arm 4I, as a result of the action of resistors 52 and 53. When the tube 44 is conducting, the added voltage is proportional to sin 0. The square waves 54 and 55 which alternately energize tubes 44 and 46 are derived from'the same source 3| but are 180 degrees out of phase. Both are synchronized with the signal supplied to the terminal "H-scan on the oscilloscope of Fig. 1 but at half its frequency as described in connection with Fig. 6. It is this half frequency synchronizing signal which also introduces the small D.I C. voltage referred to in connection with Fig. 9. Thus the shifting of the angle coincides in time with the initiation of the scan.` It will be understood that while Fig. 7 has been described in detail for producing the oscillation about cos o, the oscillation about sin 0 is likewise effected and the corresponding portions of the circuit bear the same numerals with the added letter a.

Fig. 8 shows a tube whose construction is substantially the same as that of the tube shown in Fig. 1, but in addition to the double part of plates 18, 19, and 82, 83, which correspond to the previously discusseddeflection plates 8, 9, I2 and I3, two additional pairs of deflection plates 88, 89, and 92, 93, are incorporated in the tube of Fig. 8. The second set of deflector plates 88, 89, 82, 93, is used to compensate for errors due to misalignment of the tube electrodes or due to weak magnetic iields such as that of the earth. If all deiiection plates in either Fig. 1 or Fig. 8 were grounded, it is quite possible that the electron beam would not strike exactly the center of baille electrode I4 or 84 because of the possible slight misalignment of the tube electrodes or as a result of external elds. While in the description made in connection -with Fig. l, no means have been mentioned for correct centering of the beam, attention should now be called to the fact that in practical operation it is necessary to employ external correcting means in connection with the tube of Fig. 1. They may consist of a permanent magnet or of two'sets of orthogonal coils, each provided with a separate current adjustment. In the special tube shown in Fig. 8, the necessary corrections yfor misalignment and external elds are made by means of the auxiliary electrostatic deflection plates 88, 89, 92, 93. Centering of the beam of the tube shown in Fig. 8 is obtained as follows: With the plates 18, 19, 82, and 83 grounded to the second anode, potentiometers 90 and 9| are adjusted simultaneously until the current collected by catcher 85 reaches a maximum. No further adjustments of potentiometers 90 and 9| are necessary so long as the external fields do not vary appreciably.

Instead of using the arrangement of the tube shownin Figs. l and 8, a double coincidence detector arrangement can also be obtained by using a standard cathode-ray tube of the type used, for instance, in television, in conjunction with a photocell. This arrangement will now be explained in connection with Fig. 9 in which 'numeral 94 indicates an ordinary cathode-ray tube provided with two dimensional or coordinate scanning means and preferably with means for modulating the electron beam. As can readily be understood, in the absence of scanning potentials, the fluorescent' signal appearing on the screen of the cathode-ray tube in response to the stationary electron beam will be located at a' xed point near the center of the screen when the deflection plates of each pair are at the same D. C. potential. In the absence of external elds, and if the electrodes of the tubes are perfectly aligned, the spot will appear exactly at the center of the screen. The aperture 96 of housing 95 which is made of opaque material, is now placed on the center of the uorescent screen, where the bright spot appears` The light penetrates from the bright spot through aperture 96 and is received by the photocell 91 whose electric rey sponse may be used to release a relay or to give a direct signal in an associated circuit (not shown in the figure). Photocell 91 will only receive light when the spot on the cathode-ray tube screen is at or very near to its center. If the spot is not at the center of the screen, the photocell will not respond. This will happen if the voltages applied to the deflection plates of one or both pairs are not equal. The arrangement of Fig. 9 also gives a simple method of compensating for external elds or for misalignment of the tube elements. 'Ihisadjustment can simply be carried out by removing all deflection signals and then moving the housing 95 over the face of the cathode-ray tube screen until the current from photocell 91 reaches a maximum. The housing is then clamped in this position by means not shown in the figure. Y

Instead of simulating the azimuth operations by the means of Fig. 1, a modified form is shown in Fig. l0. Referring now to Fig. 10, sinusoidal oscillations of any predetermined frequency from source are fed to two identical phasers ||J|, |02, of the type described, for instance, in my in the gure is controlled by the student and it is by means of this control that he attempts to match the setting of the master operator.

The output signals of the two phasers maybe added in any of several different ways. I have chosen two parallel triodes |03 and |04 which are operated on the linear portion of their characteristics. When the signal on the grid of tube |03 is 180 degrees out of phase with that on the grid of tube |04, no alternating current passes through the combined load circuit |05 and hence no Voltage is developed. For all other phasing conditions, however, the currents through tubes |03 and |04 do not cancel but will result in a finite current of an amount depending upon the phase difference which produces an alternating voltage across load circuit |05. This alternating voltage is rectified by tube |06 and is smoothed by the RCv circuit made up of condenser |01 and resistor |08. The direction or poling of therectier is such that with increased A. C. voltage across load circuit |05, the bias on the grid of tube |09 is increased. A fixed bias of a suitable value is applied to the grid of tube |09 by means of battery ||0. The pulse signal |34 corresponds to the signal 34 in Fig. 1. It can readily be seen that the gain of tube |09 is a function of the bias which is applied to it by the action of diode |06 and load circuit |05. the output pulse signal is controlled by the angular setting of the student shaft S relative to that of the` master shaft M. It is readily understood, of course, that the tube |09 may be a remote cut-off pentode or any other desired type of amplifier tube. By suitable selection of this tube and of bias I0, it is possible to have output signal only when the student shaft is within say copending application Serial No. 435,157, led'.

x20 degrees of the setting of .the mastershaft M. The amplitude of the output signal plotted against student phaser shaft angle can thus be made to resemble closely the response curve of Fig. 2.

The arrangement of Fig. 10 corresponds to that of Fig, 1 in that in both cases the student determines the azimuth by maximizing the height of the pulse seen on the scope. This maximum height is found by turning the student shaft S back and forth.

In order to obtain the type of display described in connection with Figs. 3, 5, 6 and 7, it is possible to make use of a circuit such as that shown in Fig. 12, although of course numerous variations are within the scope of the invention. The sinusoidal oscillations from source |20 are fed to two phasers |2|, |22. The phaser |22 controlled by the student is exactly like those previously referred to. 'I'he master phaser |2| is preferably, however, of a modified design about to be described in connection with Fig. 1l. The rotating magnetic eld is achieved in exactly the same way as in a standard phaser. .As shown in Fig. 1l, the oscillator |55 provides sinusoidal voltage to the damped resonant circuit comprising resistor |59, capacitor |58 and inductance |51, which are so adjusted as to give a magnetic field at its center exactly equal to, but in phase quadrature with that produced by coils |56. These coils are orthogonal to each other and thus produce the rotating magnetic eld The pick up coil |60 comprises a relatively large number of turns. Orthogonal to coil |60 there is another center tapped coil |6| of a smaller number of turns. Because of the orthogonal relationship and the nature of the rotating magnetic eld, the voltage developed across coil |60 is 90 degreesout of Hence, the amplitude of l phase against that developed across |6|, so that the voltage takenbetween'eontacts |62 and |63 is equal to but slightly phase shifted against that developed'betweencontacts |62 and |64. ,This phase difference is determined, of course, by the relative number of turns in, and the sizes of coils |60 and |6I. A convenient value may be 15 degrees.

Returning now to Fig. 12, the output signal of the student phaser |22 is added separately to the twooutput signals of the master phaser |2| by means of tubes |3| and |32, which have a common plate load |35, and tubes |36 and |31, which have the, common plate load |38. Rectiiiers |39 and |40 develop separate bias voltages which are determined by the plate relationships between the voltage delivered by the student phaser and each of the two voltages provided by the master phaser. These two bias voltages are supplied to the grids of two pentodes (or similar tubes) |4| and |42. nPulse signal |43 is superimposed upon the control grids of both of these tubes and in series with the previously described bias. Pulse signal |43 corresponds to signal`34 in Fig. l. Square waves |44 and |45 modulate the suppres-y sor grids of tubes |4| and |42 in phase opposition. Their amplitudes are so chosen as to cut off completely the tube to which they are applied during their negative cycles. Thus, tubes I 4| and |42 become alternately conductive. Hence, signals |44 and |45 determine which of the two developed bias voltages shall affect the size of the output signal. As shown in Fig. 12, pulses |46 are derived from tube |42, the smaller pulses |41,

from tube |4|. Therefore, the bias developed on tube |4| is greater in this instance than that on.

tube |42, indicating that the angular position of the student shaft S is different from that of the master shaft M. 'I'he two sets of signals |46 and |41 may be displayed in the manner described in connection with Fig. 6.

The invention described herein may be manufactured and used by and for the Government of the United States for governmental purposes, without payment to me or assigns of any royalty thereon.

What I claim is:

1. A double coincidence detector comprising means to develop an electron beam, a pair of beam deflector elements for deflecting the beam in one direction, another pair of beam deecting elements for deflecting the beam in a different direction, means to energize one element of the first pair under control of a signal from a standard source, means to energize the other element Iof the first pair under control of a signal from a comparison source, means to energize one ele-` ment of the second pair under control of said standard source, means to energize the other element of the second pai'r under control of said comparison, source, and means to detect when the signal from the comparison source bears a predetermined relation to the signal from the standard source.

2. A double coincidence detector according to claim l in which the last-mentioned means includes a collector electrode for the electron beam. and a baille electrode located-between said col lector 'and said deflecting elements.

3. A double coincidence detector according to claim 1, in which the last-mentioned means includes an indicating device for producing a characteristic indication when said beam, after passing said deflecting elements follows a predetermined path with respect to its pathbefore passing said deflecting elements.

4. A double coincidence detector according to claim 1, in which the last-mentioned means includes an oscillospe which is jointly controlled by the electron beam after passing said deflecting elements and by the phase relation between two sets of pulses which also control the said electron beam.

5. A double coincidence detector according to claim 1, in which the standard source includes means for generating two adjustable voltages, one

being a function of the sine of a given angular setting, and the other being a function of a cosine of that angular setting, and the comparison source has sinylar means for producing sine and cosine function voltages.

6. A double coincidence detector according to claim 1, in which the standard source and the comparison source each includes a pair of poten-- tiometers each having an adjustable tapping arm and a common operating control for simultaneously adjusting the positions of the arms to vary the potentials tapped off thereby in correlationv with different angular functions of the particular angular setting of said common control.

'7. In a double coincidence detector, an electron tube having means to develop an electron beam, beam deflecting plates arranged in oppositely disposed pairs, means to energize the plates of one pair under control of sine functions of the angular settings of two independently adjustablev control members, and means to energize the plates of the other pair under control of the cosine functions of said angular settings.

8. A double coincidence detector according to claim '7, in which the electron beam producing means is provided with a beam-modulating electrode, and means are provided to energize said modulating electrode by pulses which are derived from a standard source, and an oscilloscope is provided and connected to said tube and to said source to produce an indication jointly controlled by the voltages impressed on said pairs of plates and the pulses impressed on said modulating electrode. i

9. In an apparatus of the character described, a signal source producing a succession of pairs of impulses, means to delay the phase of one pulse of each pair with respect to the other pulse of the same pair, means to adjust the amount of said phase delay, a double coincidence detector tube having means to develop an electron beam, beam-modulating means upon which at least one of said pairs of pulses is impressed, and an oscilloscope whose deecting system is controlled by the signal from said detector tube and by the said phase delay.

10. Apparatus for teaching the manipulation and operation of radars and the like, comprising a masters device for producing an electric signal representing azimuth settings, a students device/for producing an electric signal representing azimuth settings, a masters device for pro-- ducing electric signals representing range settings, a students device for producing electric signals representing range settings, and double tector includes an electron tube having two sets 4of control members for the beam, one set being connected to the masters azimuth setting device and the other set being connected to the students azimuth setting device, said tube having additional means for controlling the production of an output signal only when the eect of one of said sets of control members is substantially neutralized by the effect of the other set.

12. Apparatus for teaching the manipulation and operation of radars and the like according to claim 10, in which the double coincidence detector includes an electron beam tube having' pairs of beam-deecting members,l one pair being energized under control of the masters azimuth signal, and the other pair being'energized under control oi' the students azimuth signal, a-ndmeans responsive to the output of said tube to produce an indication to show the relation between the two signals.

13. Apparatus for teaching the manipulation and operation of radars and the like according to claim 10, in which the double coincidence detector includes a tube for developing a beam of electrons, deiiecting means controlled jointly by the students azimuth signal and the masters azimuth signal, said beam normally following an undefiected or axial path when the two signals are substantially alike, and means responsive to deflection of said beam to determine when said signals are unlike.

. .14.. Apparatus for teaching the manipulation and operation of radars and the like comprising a pair of potentiometers, a master control device for simultaneously adjusting said potentiometers in accordance with a master azimuth setting to produce two voltages one corresponding to the sine of the azimuth angular setting the other corresponding to the cosine of that setting; an electron tube for developing an electron beam and having a pair of electrostatic deiiector plates arranged to deflect said beam in two diierent coordinate directions; means to apply said sine and cosine voltages to said plates respectively; another pair of potentiometers, a students control device for simultaneously adjusting said other pair of potentiometers in accordance with a students azimuth setting to produce two voltages one corresponding to the sine of the students azimuth angular setting the other corresponding to the cosine of that setting, another pair of electrostatic deector plates in said tube also arranged to deilect said beam in said coordinate directions, and means to apply the sine and cosine voltages from the students potentiometers to said other pair of plates respectively, and an output circuit for said tube which produces a characteristic signal when the action of the iirst two voltages on said beam is neutralized by the action of the second two voltages.

15. Apparatus for teaching the manipulation and operation of radars and the like, comprising a source of master electric pulses simulating the direct and echo pulse of a radar, a masters phase delay device, a students phase delay device, said devices being independently adjustable by the master anad student respectively to simulate range settings of a radar and the like, the masters device also including an attenuator for attenuating certain of said pulses to simulate the echo pulses, a double coincidence detector tube having means which responds to electric signals representing respectively azimuth settings of students device, and control means in said tube upon which the said master pulses are impressed together with the echo pulses, means controlled by the output of said tube for producing an indication corresponding to said echo pulses, said indication being produced only when the masters and students azimuth settings are substantially alike, the last-mentioned means being of a type which also simultaneously indicates when the settings of a masters and students range setting device are substantially alike.

16. In a radar training system and the like, a masters position, a students position, the masters position including means to develop electric signals representing azimuth settings, the students position also including means to develop electric signals representing azimuth settings, both the masters position and the students position each having means to produce a signal reppresenting range settings, an electron tube having an electron emitter, a control electrode system and an output electrode, said control electrode system being connected to the masters and students positions to cause said tube to produce an output signal which is a function of the relative settings of the masters and students azimuth setting device, means to impress on said control electrode system a plurality of successive pairs of pulses, one pulse of each pair representing a datum signal and the other pulse representing a radio echo, and an indicator device which is connected to said electron tube so as to produce an indication only when the masters and students azimuth settings are substantially alike, said indicator device also including means to produce a characteristic indication when the students range setting and the masters range setting are substantially alike.

17. A system according to claim 16 in which said control electrode system comprises a pair of horizontal beam deflecting plates, a pair ci vertical beam deflecting plates and a contrai grid, said masters position being connected to a horizontal deecting plate and to a vertical. deflecting plate, said students position being connected to the other horizontal deiecting plate and to the other vertical deiiecting plate, said control grid being connected to a source of echo pulses controlled from the masters position.

18. A system for radar training and the like, comprising a source of datum pulses, a masters position, a students position, means at said masters position to receive said pulses to produce corresponding phase delayed pulses simulating a radio echo and representing a range setting. means at said students position to receive said pulses and to adjustably phase delay them to represent the students range setting, an electron tube having a control electrode upon which at least. said echos are impressed, an oscilloscope having a pair of delecting systems, one system being controlled by the output of said tube, and the other system being controlled by the students phase-delayed pulses.

19. A system according to claim .1,8 in which said tube includes an electron beam deflecting system for deflecting the beam in one direction and another electron beam deiiecting system .for deflecting the beam in the opposite direction, one deflecting system being connected to both the masters and students positions, other deflecting system also being connected to both the masters and students positions, and means to produce a characteristic signal in the output of said tube a masters device and azimuth settings of a when the control from the masters position on Cil tem, means to energize the modulating system under control, of at least said echoes, means' to energize the deiiecting system under joint control of a masters azimuth setting device and a students azimuth device, and a cathode-ray tube oscilloscope connected for joint control by the output signal from said tube and by the setting of the students range device.

2l. A system according to claim 20 in which said cathode-ray tube detector comprises an additional beam-deflecting system which is adjusteu' to centralize the cathode-ray beam to render it independent of external stray ilelds.

22. A system according to claim 20 in which said cathode-ray tube detector has a fluorescent screen and the deilecting syst-em is such that an output signal is produced on said screen only when said beam is centralized.

23. A system according to claim 20 in which said cathode-ray tube detector has a fluorescent screen and is provided with an apertured mask l' `lit cell combination mounted adjacent the screen to produce a signal only when the cathode-ray beam is centralized.

2a. 'in a radar training system, means to produce pulses representing respectively the direct pulses from a radar antenna and the echo pulses, and means to simulate the Operation of a radar oi' the type which utilizes the overlapping field patterns of two angularly displacedy antennae, the last-mentioned means including a students azimuth setting device for deriving signals representing an azimuth to be determined, a masters azimuth setting device for deriving signals representing said azimuth setting to be determined by the student, a double coincidence electron tube detector, means to impress the said students azimuth signals and said masters azimuth signals on the electrode system of said tube, and means to impress at least said echo pulses also on the electrode system of said tube, said tube having its electrodes arranged so that it produces a characteristic signal in its output only when the students azimuth signal is substantially the same as the masters azimuth signal.

25. A radar training system according to claim 24 in which the masters azimuth setting device has means to vary the azimuth signal a predetermined small amount on either side of a mean setting to simulate the effect of two directional radar antennae.

26. A radar training system according to claim 24 in which a students phase delay device is provided for receiving and delaying said pulses to correspond with the phase delay of said echo pulses, and an oscilloscope indicator is connectedto the output of said double coincidence detector tube and to the students phase-delay device whereby the student can observe when his azimuth setting corrsponds to the masters azimuth setting and also when the phase of the students phase delayed pulses is the same as. the phase of said echo pulses.

27. A radio training system according to claim 24 in which the students azimuth setting device derives -two vo1tages for each angular azimuth setting, one voltage being a sine function and the other a cosine function of said setting.

28. A radio training system according to claim 2i in which the students azimuth setting device and the masters'azimuth setting device each' derives two voltages for its respective angular setting, one voltage being a s ine function and the other a cosine function of said setting.

29. A radar training system according to claim 24 in which the masters azimuth setting device derives two voltages for each angular azimuth setting, one voltage being a sine function and the other a cosine function of said setting, and means are provided to automatically osoillate thesine and cosine functions about a mean angle to simulate the effect of oscillation of a radar double antenna.

30. In combination, an adjustable device whose setting represents the angular orientation of an object, means responsive to the setting of said device to produce at least two voltages which are related by cosine and sine functions of said orientation, a switch responsive to at least one voltage to control the oscillation of the sine voltage about a mean value, another switch responsive to at least one other voltage for oscillating the cosine function about a mean value, and a common detector circuit connected to both switches for producing a signal which is controlled jointly by the two oscillated voltages.

31. The combination according to claim 30 in which' each of said switches is an electronic switch, and means are provided to render the switches alternately conductive in predetermined timed relation.

32. In combination, an adjustable device whose setting represents the angular orientation of an object. a potentiometer for deriving a sine function voltage of said orientation, another potentiometer for deriving a cosine function voltage, both said potentiometers being operated jointly by said device, electron switch means connected to the sine function potentiometer for producing an oscillation in the value of said sine function, other electron switch means for producing an oscillation in the value of said cosine function, a

second adjustable device, a. sine function potentiometer and a cosine function potentiometer for producing sine and cosine voltages corresponding to the angular setting of said second device. and a double coincidence detector upon which' the voltages from all said potentiometers are applied to determine when the setting of the second device corresponds to the setting of the rst device.

33. The combination according to claim 30 in which each of said switches is in the form of a pair of grid-controlled electron tubes, and a source of timing waves is connected to each pair of said tubes whereby the tubes of each pair are alternately rendered conductive.

34. The combination according to claim 30 in which each switch comprises a grid-controlled electron tube, means to apply a portion of the sine function voltage to a grid of said tube to produce an output voltage proportional to said sine funcv tion voltage, and means to combine the said cosine function voltage with said output voltage.

35. In combination, an angularly adjustable device, means responsive to a given angular setting A of saiddevice to produce a voltage represented by sin 0 and simultaneously to produce another voltage represented by cos 0, a pair of electron switches, meansto apply the sin 0 voltage to one of said switches to produce a voltage represented by :L-A sin 0, means to apply the cos 6 voltage to the other switch to produce a voltage representedl by i-A@ cos 0, means to combine the sin -0 voltage and th'e :4 -A0 cos 0 voltage, means to combine the cos 0 voltage with the im? sin 0 voltage, and a double coincidence detector on which both said sets of combined voltages are applied to determine equality or lack of equality with other sets of voltages also applied to said detector.

36. The combination according to claim 35 in which each electron switch comprises a pair of grid-controlled tubes which' are alternately rendered conductive by connection to a Vsource of timing impulses, one tube of the rst pair producing in its output A0 sin 6 voltage, and the other tube of said rst pair producing -Aa sin 0 voltage, one tube of the second pair producing A0 cos 0 voltage, and the other tube of the second pair producing A0 cos 0 Voltage.

37. The combination according to claim 30 in which the means for producing the sine and cosine function voltages comprises a pair of potentiometers whose contact arms tap oi said voltages in response to the setting of said adjustable device, each potentiometer having an additional arm for tapping 01T negative cosine and negative sine functions of said voltages.

38. In combination, a pair of potentiometers, a pair of slider contacts for each potentiometer, a common operating device for simultaneously moving both pairs of contacts to positions representing the angular settings of an object, the two contacts for one potentiometer deriving respectively a voltage sin 0 and -sin 0, the two contacts for the other potentiometer deriving respectively a voltage cos 0 and -cos 0, where 0 represents said angular setting, means to combine at regularly recurrent intervals with the sin 0 voltage an increment represented by -A0 cos 0, means to combine at regularly recurrent intervals with the cos 0 voltage increments represented by iA@ sin 0, and a common detector upon which both said sets of combined voltages are impressed.

39. The combination according to claim 38 in which said detector comprises a cathode-ray tube having coordinate beam deflecting systems upon which said combined voltages are respectively impressed.

40. In a radar trainer or the like, a students azimuth setting device, a students range setting device, a masters azimuth setting device, a masters range setting device, means responsive to the students azimuth setting device to produce sine and cosine voltages representing said angular setting, means responsive to the masters azimuth setting device to' produce sine and cosine voltages representing angular settings to be ascertained-by the student, the masters sine and cosine voltages being aried positively and negatively symmetrically about a mean angular value at regularly timed intervals, a master oscillator, a pair of phase Shifters fed from said master oscillator, one phase shifter being controlled by the students range device and the other phase shifter being controlled by the masters range device, a double coincidence detector tube having a set of four electrodes for comparing the students and masters sine and cosine voltages, said tube having another electrode for controlling the output of the tube under control of the output of the masters phase shifter, and a cathode-ray tubel oscilloscope having one deiiection system controlled by the output of said detector, and the other deection system controlled by the output of the students phase shifter.

41. A radar trainer according to claim 40 :in which the masters sine and cosine voltages are varied positively and negatively under control of a pair of electronic switches, each of said switches being controlled in synchronism with said master oscillator.

42. A radar trainer according to claim 40 in which the masters sine and cosine voltages are varied positively and negatively under control of a pair of electronic switches, each of said switches being connected to said master oscillator through a frequency subdivider.

43. In a phase comparison system, a source of master oscillations, a standard phaser and a comparison phaser connected to said source, each phaser having a control shaft, a pair of gridcontrolled electron tubes having their input circuits connected respectively to the standard phaser and the comparison phaser, a common load device connected to the output electrodes of said tubes, and means controlled by the current in said load for producing a signal only when the shaft of the comparison phaser is within a predetermined angular setting with respect to the shaft of the master phaser.

44. A phase comparison system according to claim 43 in which the said tubes are connected to add the outputs from the two phasers, and the means for producing said signal comprises a rectiiier for rectifying the load current and another grid-controlled tube whose grid is biassed under control of said rectifier.

45. A phase comparison system according tovv claim 43 in which the said pair of tubes are connected to the two phasers to add the outputs thereof, and the means for producing said signal comprises a rectifier for rectify-ing the load current and a grid-controlled tube whose grid bias is controlled by the rectified current, the rectier and grid-controlled tube being designed so that the output signal simulates the field response of a radar antenna or the like.

46. In a phase comparison system, -a source of master oscillations, a standard phaser, a comparison phaser, each being connected to said source of oscillations and each having a control shaft movable to'represent azimuth settings, the standard phaser having means to produce two series of phase-displaced signals, means to combine the signals from the comparison phaser with the two signals from the standard phaser, a pair of alternately conductive electron switches, and means connecting the control' electrodes of said switches to both said phasers to control the current through the switches in accordance with the angular relation between shafts of the two phasers.

47. A phase comparison system according to claim 46, in which the standard phaser comprises two stator windings energized at a phase difference of approximately degrees and a pair of pick-up windings on the rotor, oriented approximately 90 degrees with respect to each other andl being so connected as to give two voltages which bear a xed phase relation.

48. A phase comparison system according to claim 46 in which the means to combine the outputs from the two phasers includes a, pair of grid-controlled electron tubes whose control grids are excited respectively by the two signals from the standard phaser, and another pair ot gridcontrolled electron tubes whose control grids are excited in phase by the signal from the comparison phaser, a common output circuit for one of the rst 4pair of tubes and one ot the send pair of tubes, another common output circuit for the other tube of the nrst pair and for the 'other tubeof the second pair, respective rectiners for .said common output circuits, and respective electron switch tubes for said rectiers. f

ROBERT M. 

